AbstractThe comparison of coincident daily records of the concentration of chlorophyll a (Chla) derived from the Sea-viewing Wide Field-of-view Sensor and the Moderate Resolution Imaging Spectroradiometer can provide the distribution of the standard deviation sigma associated with the zero-mean random component of the uncertainty budget. The proposed approach does not quantify the bias characterizing the Chla satellite product, but it is spatially and temporally resolved and thus appears as a useful complement to validation exercises with in situ data. The global median of sigma is equal to 0.074 for log-transformed Chla. The values of sigma that are around or larger than 0.1 are found in a significant part of the ocean, including the centers of the subtropical gyres, some Arctic and Antarctic areas, or eastern boundary upwelling regions. In general, sigma increases at the low and high ends of the Chla range, whereas it is lowest in the interval 0.1-0.3 mg . m(-3).